My first alternative keyboard project was to create a MIDI controller in the form of an isomorphic keyboard, as described in my previous post.

This project came in in two halves, Hardware on the one hand, and Software on the other. This was a bit of a chicken-and-egg situation – I needed hardware with the type of output that could be interpreted by one of my software programs; but I needed a software program that could deal adequately with the type of output the hardware – a two-dimensional key layout – would produce.

This post is about the hardware (a QWERTY keyboard).

The hardware requirement was for an input keyboard capable of playing about 40 – 50 notes, like the AXiS pictured in my previous post – the keys would be in 4 or 5 rows and the rows would have to be offset, to make it easy to press keys on more than one row at the same time, and to allow diagonal movements for melodies and arpeggios.

Apart from the physical appearance, I was looking for something simple and inexpensive – i.e. I could construct it without advanced carpentry, metal work and electronic skills, or buy it off eBay.

The third requirement was that it should connect easily to the computer.

I bought and tested some tiny ‘tactile’ switches (cheap in bulk from China), but hadn’t at that time resolved the problem of how to get the computer to understand their output; so I put them away for future use.

In fact, my conclusion was that what I needed would look very much like a computer keyboard, with rows of offset buttons, so I looked around and identified what I thought would be the most suitable. The model I chose was the Cherry G84-4100.

The reasons I chose it were a) it’s quite small and light (282 x 132mm, and 500g), but the keys are a reasonable size, b) it’s flat, making it easier to play as a music keyboard, c) it has 5 rows of equal-size keys (the top row, the F keys, are a smaller size than the others on the majority of keyboards), and d) there were quite a few available for about £15 new, £5 second-hand, on the internet. (The full price seems to be about £50, but there’s no need to pay that much, there always seem to be some for sale at a lot less).

There are several different models of G84-4100, but I don’t think the differences between them are significant, except for one thing: seeing the PS2 adapter in the picture reminds me that although most versions are USB, some versions have PS2 conectors.

USB is the ideal connection method: modern computers all use it, and music programs understand it; but if you want to do this and happen to get hold of a keyboard – or any other input device, for that matter – with a PS2 to USB connector, it can be converted. Not necessarily with a simple adapter like the one in the picture, however, which just physically changes the plug: these can’t be guaranteed to work, and you’ll probably need the kind of converter with some circuitry in it, and some of these work better than others.

I’ll be discussing interfacing ‘HID’s (‘Human Interface Devices’ – i.e. keyboards, mice, joysticks and so on) in more detail in later posts, but if this happens to be an issue for you at the moment, this: http://geekhack.org/showwiki.php?title=PS2-to-USB+adapters is the best discussion on the internet of the alternatives.

[Edit: this link seems to be dead now, but there are lots of discussions of this topic on that forum].

I use this one, the so-called ‘Blue Cube’. It can be found at a reasonable price on eBay, but try and avoid PS2 if your computer doesn’t have a PS2 socket, as a decent converter like this one may cost as much as the keyboard.

[Edit: a more recent post on the geekhack forum recommends this type of connector, rather than the Blue Cube:

It’s said to be much cheaper, but doesn’t always work on Macs. The Blue Cube seems to work fine on all my Macs].

So, I got the keyboard. Any keyboard will do, if you’re doing this, so you could just as well use any type – including the one that came with your computer, obviously. I wanted a separate one because it would be more convenient than the laptop (and had the full-size 5th row of keys), it would look better, and could be customised, if required.

In my case, I customised it by prising the keys off and painting them red, as I found the letters and numbers distracting. (I should mention at this point that I didn’t do this until I had sorted out the software set-up, which I’ll describe in my next post: it was helpful to know which key was which during the process of getting the computer program to interpret the keys in the way I wanted!)

The keys on this particular model are Cherry ML (not their more well-known MX type, but more suitable for this application, being flatter in profile). Replacement keyboard caps are available (from http://uk.rs-online.com/web/p/switch-accessories/0199447/), but I wouldn’t bother with those unless you break or lose a large number of the originals, as they’re pretty expensive!

You can also get a special tool for getting the keycaps off gently, but you don’t need it if you’re careful, or don’t want to get the keycaps off at all – and it’s also unnecessarily expensive. I wanted to take the caps off not just to paint them, but to clean the keyboard, as it was second-hand. The can of paint was only £1 from the Poundshop, so wasn’t a major expense.

If you do want to take the keycaps off, the best thing is to use two small screwdrivers or similar tools, one under each side, to lever them off with equal pressure on each side. They just pop off and press back in place, and unlike many keyboards, nearly all of them are identical. There are a few that are slightly bigger or smaller, and it’s generally obvious which ones; there are also a few – for example the space bar – which also have a little metal bar which you have to put in place before pressing the keycap back on.

At this point I had the keyboard I needed – not quite as nice as the AXiS, I know, but I was sure it would work in much the same way. Next I needed to pick the software to use it with. This will be the subject of my next post.

Yes, unfortunately, that’s correct! It’s really a cheap and simple way to experience isomorphic keyboards before deciding whether you want to spend money on, for example, an Axis 49 or Axis 64. These, of course, are polyphonic and velocity-sensitive.